1. Field of the Invention
The present invention relates to mesoporous structures.
2. Description of the Prior Art
The International Union of Pure and Applied Chemistry, IUPAC, classifies porosity on the basis of pore diameter, dp. Mesoporous materials are defined by IUPAC as those materials in which 2 nm mesoporous inorganic materials comprise inorganic xerogels (e.g., the common silica desiccants), pillared clays, and the subject matter of this application. Mesoporous molecular sieves (MMS), discovered by researchers at Mobil, are described in U.S. Pat. No. 5,098,684, issued to Kresge et al. on Mar. 24, 1992, and U.S. Pat. No. 5,057,296 issued to J. S. Beck on Oct. 15, 1991, the entire contents and disclosures of which are hereby incorporated by reference. These materials are referred to in the literature as the MCM (Mobil composition of matter) family of materials. MMS prepared generally as powders have received enormous attention by the research community since their announcement by Kresge et al. (Kresge C. T., Leonowicz M. E., Roth W. J., Vartuli J. C., Beck J. S., Nature, 1992, 359: 710-712, the entire contents and disclosure of which is hereby incorporated by reference). In the past two years, advances have been made in understanding and exploiting the supramolecular templating process used in MMS formation, development of new synthetic procedures, extending the compositional range beyond silicas, and processing of MMS as thin films. MMS are high surface area amorphous solids (with surface areas up to 1400 m2/g) characterized by monosized cylindrical pores, ranging from about 12-100 Å in diameter, organized into periodic arrays that often mimic the liquid crystalline phases exhibited by surfactants. MMS synthesis procedures typically require four reagents: water, surfactant, a soluble inorganic precursor, and a catalyst. MMS form (as precipitates) in seconds to days (Beck J. S., Vartuli J. C., Roth W. J., Leonowicz M. E. Kresge C. T., Schmitt K. D., Chu C. T. W., Olson D. H., Sheppard E. W., McCullen S. B. et al., J. Am. Chem. Soc., 1992, 114: 10835; Huo Q., Margolese D. L., Ciesla U., Demuth D. G., Feng P., Gier T. E., Sieger P., Firouzi A., Chmelka B. F., Schuth F., Stucky G. D., Chem. Mater., 1994, 6: 1176-1191, the entire contents and disclosures of which are hereby incorporated by reference) at temperatures ranging from 180° C. to as low as −14° C., depending on the inorganic precursor. Before pyrolysis or surfactant extraction, pure silica MMS exhibit three structure types: (1) hexagonal (referred to as H or MCM-41), a 1-d system of hexagonally ordered cylindrical silica channels encasing cylindrical surfactant micellar assemblies; (2) cubic (C), a 3-d, bicontinuous system of silica and surfactant; and (3) lamellar, a 2-d system of silica sheets interleaved by surfactant bilayers.
Over the past several years, various MMS synthetic pathways have been elucidated (Beck J. S., Vartuli J. C., Curr. Opinion in Solid State and Material Science, 1996, 1: 76-87, the entire contents and disclosure of which is hereby incorporated by reference). Experimentally, it has been shown that MCM-41 type phases form under conditions in which the surfactant—before the addition of the silica source—is free (surfactant concentration is less than the critical micelle concentration for spherical micelles). In the past several years, there has been synthesized multicomponent and non-silica MMS (Huo Q., Margolese D. L., Ciesla U., Demuth D. G., Feng P., Gier T. E., Sieger P., Firouzi A., Chmelka B. F., Schuth F., Stucky G. D., Chem. Mater., 1994, 6: 1176-1191, the entire contents and disclosure of which is hereby incorporated by reference) for catalytic applications due to their higher surface areas and greater accessibility of active sites compared to zeolites.
In the past few years, various pathways have been explored to access a wide spectrum of mesostructured materials with tunable pore sizes and arrangements (orientation) and good compositional control. These materials include ionic, covalent and electrostatic interactions, and they permit the addition of salts and auxiliary solvents. A variety of macro- and microstructures have been synthesized such as powders, fibers, monoliths, thin films, hollow and transparent hard spheres, and aerosol particles, which find applications in catalysis, membrane separation, sensors, optoelectronics and as novel nanomaterials, see Jackie Y. Ying, C. P. Mehnert, M. S. Wong, Angew. Chem. Int. Ed., 1999, 38, 56-77; C. J. Brinker, Curr. Opin. Solid State Mater. Sci., 1, 798-805, 1996; J. C. Vartuli, C. T. Kresge, W. J. Roth, S. B. McCullen, J. S. Beck, K. D. Schmitt, M. E. Leonowitz, J. D. Lutner, E. W. Sheppard, Advanced Catalysts and Nanostructured Materials: Modern Synthesis Methods (Ed: W. R. Moser) Academic Press, New York, 1-19(1996); G. D. Stucky, Q. Huo, A. Firouzi, B. F. Chmelka, S. Schacht, I. G. Voigt Martin, F. Schuth, Progress in Zeolite and Microporous Materials, Studies in Surface Science and Catalysis, 105, (Eds: H. Chon, S. K. Ihm, Y. S. Uh), Elsevier, Amsterdam, 3-28, (1997); N. K. Raman, M. T. Anderson, C. J. Brinker Chem. Mater., 8, 1682-1701, 1996; D. M. Antonelli, J. Y. Ying, Curr. Opin. Coll. Interf. Sci., 1, 523-529, 1996; D. Zhao, P. Yang, Q. Huo, B. F. Chmelka and G. D. Stucky, Current Opinion in Solid State & Materials Science, 3,111-121, 1998; Y. Lu, H. Fan, A. Stump, T. L. Ward, T. Rieker, C. J. Brinker, Nature, 398, 223-226, 1999, the entire contents and disclosures of which are hereby incorporated by reference. However, none of these processes provide an ability to design these materials with a controlled combination of mesophases or the ability to pattern functionality.